1. Field of the Invention
The present invention relates to electronics and electrical systems. More specifically, the present invention relates to systems utilizing GPS (Global Positioning System) signals.
2. Description of the Related Art
Many applications using GPS for navigational purposes, particularly handheld applications, require low power in order to preserve battery life. The primary components that dissipate large amounts of power are signal processing ASICs (application specific integrated circuits) including digital signal processors (DSPs) that are required to acquire and track the GPS signal. Many power requirements are difficult if not impossible to meet given the current state of semiconductor technology combined with requirements for steady navigation updates (i.e. updates required every second or two). The key dilemma is that hardware components need to be continually powered on in order to track and produce navigation updates at the required rate.
Prior attempts to solve the problem have focused on adding low power improvements to the hardware. With each new generation of DSP technology, shrinking semiconductor geometries result in processors with lower amounts of power dissipated when operating continuously. In addition, recent DSP innovations have produced low power “shutdown” modes that enable users to shut off clocks to the DSP core on a programmable basis, virtually shutting off the DSP in the process. Conventional tracking techniques, however, require continuous tracking of the GPS signal. These traditional tracking techniques fundamentally limit the amount that new DSP “shutdown” features can be utilized since continuous track is required.
Conventional GPS tracking systems utilize classical phase and delay lock loops that require a continuous stream of GPS signal samples in order to track the signal and form measurements that are input to the navigator. This standard tracking technology cannot be interrupted for periods of time without having to reacquire the signal and re-establish a steady state condition (which typically requires several seconds). Therefore, it is not possible to switch the signal processing hardware from on to off and back on without creating a performance degrading transient condition.
Hence, a need exists in the art for an improved GPS tracking system that offers lower power dissipation than conventional approaches.